The present invention relates to an optical network, a node apparatus, and a method for relieving a path fault. More specifically, the present invention relates to an optical network, a node apparatus, and a method for relieving a path fault, which use performance monitoring and alarm transfer for relieving a fault.
A sharp increase in data traffic typified by the Internet in recent years is making the transmission capacity of a communication network larger. At present, optical transmission is advancing, intending to increase its capacity using a time division multiplexing technique or an optical wavelength division multiplexing technique. A transmitter of 10 gigabits per second for one channel has been practically used. There has also been practically used a point-to-point wavelength multiplexing transmission apparatus which performs wavelength-multiplexing for several channels to several tens of channels by one fiber and uses optical amplifiers and regeneration repeaters to permit long distance transmission exceeding several hundred kilometers.
To respond to future demand increase, further economization, and service diversity, a ring optical network which ring-connects connection nodes and a mesh optical network which mesh-connects them to increase connectivity are being studied. Such optical networks are used together with a monitoring control system which remotely and integrally manages node apparatuses, thereby expected to facilitate end-to-end path management from the start point to the end point of a line and to make path setting faster. The control units of node apparatuses are in conjunction with each other, thereby expected to facilitate end-to-end path management from the start point to the end point of a line and to make path setting faster. The mesh optical network can select a necessary line when the spare capacity in a mesh network is required. The spare capacity can be shared between plural working paths to economically realize the entire network.
To realize the mesh optical network, an optical signal switching apparatus and an optical cross connect apparatus which can switch, an optical signal such as STM-64/OC-192 and 10 GbE and perform path switching and switching to a stand-by system are being developed. The optical cross connect apparatus can switch the connection between transmission paths connected to a node or the connection relation between a transmission path and a user device in an distribution control method or a centralized and remote control method. An O-E-O (optic-electronic-optic) type optical cross connect system which uses light as optical input/output and performs signal processing by an electric signal performs processing by an electronic circuit in a transmission unit, for instance, in an STS-1 unit finer than STM-64 or OC-192. Efficient signal switching can be done.
An O-O-O type optical cross connect system which performs switching using an optical switch without converting an optical signal to an electric signal is expected to process a large amount of information difficult to be realized by an electronic circuit, for the increased amount of node processing information.
As an example of a circuit recovery method in the mesh optical network, Document 1 describes a method of dividing an optical path into segmented paths having plural nodes and at least one link to perform efficient circuit recovery using the optical cross connect system.
As a distributed control method in which network element control units communicate with each other to perform network status information exchange and path calculation, a network management system can be omitted or simplified. As such inter-node communication control technique, the Internet engineering task force (IETF) can use a signaling protocol of GMPLS (generalized multi-protocol label switching) defined by RFC shown in Documents 2 to 4.
Document 5 describes tandem connection monitoring (TCM) which can accumulatively perform performance monitoring by the bit interleaved parity (BIP) operation of a signal across plural nodes.
[Document 1] Japanese Patent Laid-Open No. 258851/2003
[Document 2] L. Berger, “Generalized Multi-Protocol Label switching (GMPLS) Signaling Functional Description”, January, 2003, IETF
[Document 3] P. Ashwood-Smith et al, “Generalized Multi-Protocol Label switching (GMPLS) Signaling Constraint-based Routed Label Distribution Protocol (CR-LDP) Extensions”, January, 2003, IETF
[Document 4] L. Berger, “Generalized Multi-Protocol Label switching (GMPLS) Signaling Resource Reservation Protocol-Traffic Engineering (RSVP-TE) Extensions”, January, 2003, IETF
[Document 5] ITU, “Interfaces for the Optical Transport Network (OTN)”, ITU-T, G.709/Y.1331, March, 2003
There are faults other than cable disconnection, for instance, (1) deterioration of an optical signal-to-noise ratio due to an increase in transmission path loss, noise of an optical amplifier, and a nonlinear effect in a transmission path fiber, (2) signal quality deterioration observed as a bit error due to waveform deterioration of chromatic dispersion and polarization mode dispersion of a transmission path fiber, and (3) a fault of a switching node. Due to such faults, there are the following problems in switching to a spare path executed by the mesh optical network. In the description of Document 1, a node has a switching function to a spare path, and when a preliminary resource connected to the node is shared between working paths and been has already used for recovering a fault on the working path (exhaustion of the preliminary resource) and a fault occurs on the spare path (the spare path is abnormal), another switching node is specified to perform spare path re-calculation for recovery on another spare path to reset a fault detection section. A specific procedure before and after resetting the fault detection section has not been clarified.
Here, assume that a working path section in which a fault occurs is switched to a spare path shared between plural working paths or currently-used segmented paths. In this case, to reduce processing of spare path recalculation or re-search on a working path or a currently-used segmented path in which no fault occurs, when the working path section in which a fault occurs becomes normal, returning the spare path to the original path, that is, switching-back is effective. Document 1 has not considered switching-back. The normality recovery check of the path in which a fault occurs is difficult.